1. Purpose of the Invention
The present invention is related to optical beam diagnostics and, in particular, to an optical beam diagnostics device and method utilizing coherent optical fiber bundles to characterize dynamic moving or stationary optical beams.
2. Discussion of Related Art
Beam profilers or beam diagnostic instruments are utilized, for example, to characterize the spatial, temporal, focus, and power characteristics of optical beams incident on a print plane in a laser or LED printer. Further, beam profilers can also be utilized to characterize the optical beams of laser scanners for defect scanning, bar code scanning, or other physical measurements. There are commercially available beam diagnostic instruments, such as the BeamPro or the Dynamic BeamProfiler, both produced by Photon, Inc., for dynamic or moving optical beams, such as those in laser printers, for example. In these instruments, the optical beams of the laser head in a laser printer are measured directly with the CCD or area sensor positioned at the focal plane of an optical system.
An examplary conventional beam profile head 64 that can be utilized in a beam profiler system is illustrated in FIG. 7, which shows two views of beam profile head 64. As shown in FIG. 7, beam profiler head 64 includes a plurality of individual charge coupled devices (CCDs) or other area array sensors 60 positioned along a line. Each of the individual sensors 60 are mounted on a mount 62 that can, for example, be positioned to receive light from a scan line of a print head.
FIG. 8 illustrates a raster scan of a beam 30 along a scan line 21 in an image plane 20. Such a raster scan can, for example, represent the optical output of a laser print head. Typically, the beam is modulated resulting in individual pulses 80 along an actual beam path 82 as beam 30 is raster-scanned along scan line 21. As is illustrated, two problems can be immediately discerned: bow and linearity. The bow of beam 30 describes the divergence of beam path 82 from scan line 21. The linearity refers to the variation in the spacing of individual pulses 80 along scan line 21.
As shown in FIG. 7, current beam profile heads can be problematic. For example, beam profile head 64 includes multiple area arrays 60, each of which requires individual readout and analysis circuitry for each array. Further, it is difficult to acquire the data in all area arrays 60 in one frame.
Additionally, each area array 60 is mounted in a holder that limits how close each array 60 can be to a neighboring array 60. As a result, there are limitations on which sections of a scan line 21 can be monitored by profile head 64. Further, each individual array 60 is mounted on substrate 62. Normal tolerances for such mounting results in a variation in the height of each array 60 with respect to substrate 62. This results in the fact that not all of individual arrays 60 will lie in image plane 20, resulting in variations in measuring beam 30 in beam path 82.
In addition to dynamic beams, there are other scanning slit systems for measuring static beams, such as in an LED printhead, or for characterizing beams in dynamic scanning systems such as defect scanners by static positioning of the beam. Profiles are measured directly with the scanning slit positioned at the focal plane of an optical system. A scanning-slit profiling method to characterize LED print heads is discussed in C. K. Kamimura and Y. Aiko in “High Resolution LED Print Head”, OKI Technical Review, Vol. 64, pp. 61-64, August 1998. U.S. Pat. No. 5,155,790, entitled “Electronic Scanner or Printer with Ordered Fiber Optic Array” discloses an electronic scanner or printer that employs a plurality of light conduits. Additionally, examples of applications of optical fibers or optical fiber bundles may be found, for example, in U.S. Pat. No. 4,323,925, entitled “METHOD AND APPARATUS FOR ARRAYING IMAGE SENSOR MODULES,” U.S. Pat. No. 4,441,817, entitled “ELECTRO-OPTICAL SENSORS WITH FIBER OPTIC BUNDLES,” U.S. Pat. No. 4,650,280, entitled “FIBER OPTIC LIGHT TRANSFER DEVICE, MODULAR ASSEMBLY, AND METHOD OF MAKING,” and U.S. Pat. No. 5,550,380, entitled “RADIATION IMAGE DETECTING APPARATUS INCLUDING BUNDLED OPTICAL FIBERS.”
However, it is desirable to provide a beam diagnostic device that is both easily aligned and provides simultaneous measurement of a static or dynamic beam for a full characterization of the optical beam.